mpc8xx: remove rbc823 board support

This board is old enough and has no maintainer.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/doc/README.scrapyard b/doc/README.scrapyard
index 017c25b..fe666a5 100644
--- a/doc/README.scrapyard
+++ b/doc/README.scrapyard
@@ -11,6 +11,7 @@
 
 Board            Arch        CPU            Commit      Removed     Last known maintainer/contact
 =================================================================================================
+rbc823           powerpc     mpc8xx         -           -
 quantum          powerpc     mpc8xx         -           -
 RPXlite_dw       powerpc     mpc8xx         -           -
 qs850            powerpc     mpc8xx         -           -